Pernum disclosed a goniometer instrument having vernier scale in this German Pat. No. 2,359,487, which includes a plumb plate rotatably mounted in a meter casing having a weight, preferably made of lead and having a thickness fixed in a wall of the plumb plate and has the following defects:
1. The vernier scale is separated from the main angle scale with a distance to thereby easily cause strabismal reading error.
2. The weight has an appreciated thickness and is preferably made of metallic lead so that it may increase the friction with its environment during its oscillation and may affect the optical transparency or esthetical meaning because of the clumsy thick opaque weight.
3. The angle must be read in situ to cause reading inconvenience and once the meter is uncarefully moved, the indicating angle will be fluctuated to influence the reading precision.
The present inventor has found the defects of conventional goniometer and invented the present precise-reading angular level.